1. Field of the Invention
The present invention relates to gypsum compositions for making gypsum containing materials, such as, “wallboard” and “drywall.”
2. Background Art
Gypsum wallboard, sometimes referred to as “drywall” or “plaster board” is one of the most common materials used in the construction of walls and other barriers. A common method of producing wallboard is to sandwich a core containing an aqueous slurry of gypsum between two sheets of board cover paper. Gypsum is also commonly known as stucco and calcium sulfate hemihydrate. The term “gypsum”, unless specifically stated otherwise, will be understood to include calcium sulfate hemihydrate, calcined gypsum, stucco and gypsum. In one wallboard manufacturing process, the aqueous slurry of gypsum and other wallboard ingredients are continuously deposited under high speed conditions to form a core between two continuously supplied moving sheets of cover paper. Various types of suitable cover paper are known in the art.
After the gypsum slurry is deposited between the two cover sheets, it is then allowed to set (react with water to form calcium sulfate dihydrate) to form the wallboard core. The continuously-produced board may then be cut into panels of a desired length (for example, eight feet). The boards may then be passed through a dryer to remove any excess water in the core and the gypsum is brought to a final dry state. After the core has set and is dried, the sandwich becomes a strong, rigid, fire-resistant gypsum wallboard. Other methods for the production of gypsum wallboard are described, for example, in the Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 21, pages 621-24 (Second Edition 1970) and Vol. 4, pages 618-19 (Fourth Edition 1992), and U.S. Pat. No. 5,879,446 the disclosures of which are hereby incorporated herein by reference.
In order to facilitate the production of wallboard and/or provide beneficial properties to the final product, various additives may also be included in the core gypsum slurry. For example, starch, set accelerators and/or set retarders, preservatives, and fiberglass may be included. Since wallboard is used in construction, it is desirable to prevent prolonged exposures of the wallboard to water and moisture. Certain “water repellancy,” additives/agents, such as wax, have been used in order to improve the water repellancy of the wallboard. Wax, however, can be relatively unreliable and somewhat costly.
Accordingly, it would be advantageous to provide wallboard having water repellancy without producing the deleterious effects found in the prior art.